Self-healing polymers and fiber-reinforced polymer composites (also referred to herein as “smart” polymers or materials) possess the ability to heal in response to damage wherever and whenever it occurs in the material. The damage may be caused by fatigue, impact, puncture or corrosion. These polymers are classified into two categories: intrinsic self-healing ones that able to heal cracks by the polymers themselves, and extrinsic in which a healing agent has to be pre-embedded in the material. These smart materials, which can intrinsically correct damage caused by normal usage, are expected to lower costs of a number of different industrial processes through longer part lifetime, reduced maintenance and down-time, reduced inefficiency caused by degradation over time, as well as reduced replacement costs caused by failed material.
From a molecular perspective, traditional polymers fail through cleavage of covalent bonds in the polymers. While newer polymers can yield in other ways, traditional polymers typically yield through homolytic bond cleavage (where each of the fragments of a molecule retains one of the originally-bonded electrons) or heterolytic bond cleavage (where both of the electrons involved in the original molecular bond remain with only one of the fragment species). The energy needed to break the polymer bond can be provided via different formats including kinetic, electrical, mechanical, chemical, radiant and thermal. For example, the factors that can affect how a polymer will fail include: the type of stress, the molecular structure of the polymer and the macro-level properties exhibited by the polymerized material, as well as the level and type of external excitations including solvation (the process of attraction and association of molecules of a solvent with molecules or ions of a solute), radiation and temperature.
From a macromolecular (the very large molecule commonly created by polymerization of smaller subunits) perspective, stress induced damage at the molecular level leads to larger scale damage called micro-cracks. A micro-crack is formed where neighboring polymer chains have been damaged in close proximity, ultimately leading to the weakening of the polymeric material as a whole.
Plastic cable ties (also referred to herein as “cable fasteners”) currently in use have two common forms: a two piece cable tie and a one piece cable tie. Typical two piece cable ties can include a plastic strap and a steel barb. When fastened around a bundle of wires, the steel barb engages the strap to lock the cable fastener and prevent its release. A one piece cable tie that is constructed entirely of plastic can include a plastic pawl that locks with the zig-zag surface of the strap to secure the cable tie after it is fastened. The steel barb is one main weakness of the two piece cable tie that contributes to its failure. It is known that the steel barb may bend backward to release the strap (a failure of the product) before the design strength is reached for the plastic strap. The plastic pawl of the one piece cable tie is also a main weakness. The plastic pawl can be ripped off its position to release the plastic strap. The detached plastic pawl also becomes a potential particle contaminant.
Electrical conduit is made of metal or non-metallic materials. Existing connections are threaded or use a set screw or other locking mechanism to secure the pipe to the fittings. Plastic or non-metallic connections can also be sealed using glue, an O-ring, sealant or solvents. Disadvantages of the current methods are that threads or mechanical connections may loosen over time or may be installed incorrectly. Solvents, an O-ring, sealant or glue are inconvenient to use and must be applied correctly to attain a good bond.
The heavy-duty corrosion-resistant electrical conduits and fittings currently in use are typically fabricated with metallic pipe and surface polymeric coatings. Current coating materials include polyvinyl chloride, epoxy resin, polyurea, polyurethane, polyester, acrylic derivative and modifications of these polymers. During the transportation, installation and operation of the conduit or fitting, the conduits and fittings may be damaged causing small cracks or cuts on the plastic surface. These small cracks and cuts are difficult to notice before a more severe problem occurs, such as corrosion of the metallic pipe. After the damage is identified, the repair requires a person to visit the location and manually replace or repair the conduit or fitting surface. Conventional coated conduits and fittings require extensive maintenance during the life of the product.
Explosion proof and/or hazardous location fittings currently being used typically use two part epoxy putty material as the sealant. One such filler material currently being used is CHICO® SS2 Speed Seal™ explosion-proof compound sold by Crouse-Hinds. Filled epoxy is a popular thermoset due to its high resistance to an explosion. To install the epoxy putty sealant, the two putty materials are mechanically mixed into a uniform composition. The mixed material is then cured into a polymerized form and function as a sealant. Typically, an ambient temperature of 25° C. or above is required to mix the two parts and to cure the mixed material. This temperature requirement poses a big challenge for the fitting products installed in cold outdoor environments. In one scenario, a heated tent is used in cold conditions to meet the temperature requirement. The hand mixing of the two putty materials is another labor intensive step in the installation. The uniformity of the mixture, which affects the resulting sealant performance, is difficult to achieve for two putty materials.